Geography Reference
In-Depth Information
2.1. Storage
In order to store the results of interpolation, a grid was laid out over
Germany. At present, the GCPS use about 565 MSs to represent an agri-
cultural area of aprox. 200.000 km
2
, or an average of one MS per 350 km
2
.
With the new GIS method, grid cells have a size of 1 km
2
and, after inter-
polation, are represented by virtual MSs (Liebig and Mummenthey, 2002).
2.2. Spatial Data of Temperature and Relative Humidity
For the interpolation of temperature and relative humidity the multiple
regression method was chosen because it gave the best results by the shortest
calculation time of all tested interpolation methods. The first calculations with
the four interpolation methods (Inverse Distance Weighted, Spline, Kriging
and Multiple Regression) showed that deterministic interpolation methods
were not suitable. The general purpose of multiple regressions (the term was
first used by Pearson, 1908) is to learn more about the relationship between
several independent or predictor variables and a dependent or criterion
variable. MR is an interpolation method that allows simultaneous testing and
modelling of multiple independent variables (Cohen, et al., 2003).
Parameters that have an influence on temperature and relative humidity,
e.g. elevation, slope, aspect, can therefore be tested simultaneously. MR uses
matrix multiplication and only variables with a defined minimum influence
that will be included into the model. The result of MR is a formula (x = const
+ A1*const1 + A2*const2+ A3*const3+…+ Ax*const) which allows a
calculation of a parameter set for each grid cell from which independent
variables are known (Zeuner, 2007).
To validate the results of the interpolation, 13 MSs were ignored in the
interpolation process. After interpolation, the deviation between calculated
values and measured data of these stations were compared. The study was
conducted from January to August in the years 2003 to 2006. For all stations,
MR gave results with highest accuracy (Table 1). In all cases, the coefficient
of determination (CoD) ranged between 96 and 99% for temperature and 92
and 96% for relative humidity, respectively. For the 13 MSs, the mean
deviation for temperature was less than 0.1°C and for relative humidity less
than 0.6% as calculated with MR. The absolute maximum and minimum for
temperature was less than 4.7°C and for relative humidity less than 32.6%.
The data also were tested for significance between calculated and measured
